This invention relates to an acoustic microscope technique and apparatus for non-destructive testing of an interface between two materials by spatially scanning ultrasonic waves through the material to the interface and detecting resultant leaky waves produced at the interface for determining flaws in the interface.
The construction and operation of acoustic microscopes for non-destructive testing is known from U.S. Pat. Nos. 4,459,852; 4,503,708; 4,658,649; 4,541,281; 4,655,083; and 5,079,952, for example. The teachings of these patents are incorporated herein by reference as showing examples of acoustic microscopes and components thereof which may be useful in carrying out the instant invention.
When a guided ultrasonic interface wave travels along the interface between two materials it radiates acoustic energy from each point on the interface, and forms a displacement field at the outer surface of the material.
The acoustic microscope technique for examining interfaces is noninvasive and nondestructive. Spatial scanning of the radiating energy passing through the cladding material produces an image of the interface. The resolution of the image depends on the propagation parameters of the leaky waves. An asymptotic leakage angle, the phase and group velocity (energy flow), and the attenuation (the imaginary part of propagation) vary with the wavelength for a fixed diameter rod. These parameters were calculated for each radial-axial mode for the dispersive geometry of an infinitely thick cladded rod. A variety of wave behavior was verified experimentally on samples of silicon carbide rods and steel rods embedded in an aluminum matrix.
The following is a brief review of the experimental achievements in the field of leaky, axisymmetric modes in infinitely thick clad rods.
Application of Stoneley and leaky interface waves are known for the purpose of evaluating the physical and mechanical properties of interfaces because these waves are ideal for the detection of disbonds and inclusions at interfacial bondlines. E. Drescher-Krasicka, J. A. Simmons, and H. N. G. Wadley, "Guided Interface Waves," QNDE 6B, 1129-1136 (1986); W. L. Pilant, Bull. Seism. Soc. Am. 62, 285-299 (1972); R. Yamaguchi and K. Sato, Bull. Earthquake Res. Inst. Tokyo Univ. 33, 549-559 (1955); D. A. Lee and D. M. Corbly, IEEE Trans. Sonics Ultrason. SU-24, 206-212 (1977). Others have described the importance of leaky and Stoneley waves in ultrasonic signal processing devices. Bertoni has related Stoneley and leaky wave propagation characteristics to the effect of the coupling layer on the efficiency of wedge transducers. Experimental observations of ultrasonic waves at solid-solid interfaces have been reported as shown by R. O. Claus and C. H. Palmer, Appl. Phys. Lett. 31, 547 (1977); R. O. Claus, First Int. Symp. Ultrason. Matls. Charact., Gaithersburg, Md. (1978); R. O. Claus and R. A. Kline, J. Appl. Phys. 50, 8066 (1979); H. A. Kunkel and B. A. Auld in Ultrasonic Symposium Proceedings, Atlanta, edited by McAvoy (IEEE, New York, 1983); K. D. Bennett, S. J. Hanna, and R. O. Claus, in IEEE 1985 Ultrasonic Symposium Proceedings, San Francisco, edited by B. R. McAvoy (IEEE, New York, 1985); B. S. Jackson, R. G. May, and R. O. Claus, in Proceedings of IEEE Southestcon 84, edited by B. R. McAvoy (IEEE, New York, 1985); K. Tajima, Electron. Lett. (UK) 27(3), 251-253 (1991); F. Leomy, et al., J. Appl. Phys. 67, 1210-1218 (1990); and S. I. Rokhlin, J. Phys. (Paris) 46, (C-10), 805-808 (1985).
Mode conversion has been used to and from Rayleigh surface acoustic waves (SAW) to generate and detect leaky interface waves on steel-aluminum and titanium-aluminum planar and cylindrical interfaces. It has been shown that an interface wave guided by a thin polymer film between two solids is capable of localizing the energy of elastic waves near the interface. In most of these applications, optical receivers were used as the detectors of the interface waves. S. I. Rokhlin, M. Hefets, and M. Rosen, J. Appl. Phys. 51, 7 (1980); S. I. Rokhlin, M. Hefets, and M. Rosen, J. Appl. Phys. 52, 4 (1981).
Ultrasonic measurements on a cylindrical model sample have been compared with the theoretical calculations of the dispersion relation for weakly leaky radial-axial aluminum-steel interface modes and good agreement was found between calculated and measured values. E. Drescher-Krasicka, J. A. Simmons, and H. N. G. Wadley, "Guided Interface Waves,)" QNDE 6B 1129-1136 (1986); J. A. Simmons, H. N. Wadley, E. Drescher-Krasicka, M. Rosen and T. M. Hsieh, "Ultrasonic Methods for Characterizing the Interface in Composites," QNDE 7 XX-XX (1987); H. N. G. Wdley, J. Simmons, and E. Drescher-Krasicka, "Ultrasonic Propagation at Cylindrical Metal-Ceramic Interfaces in Composites," in Proceedings of the MRS Symposium High Temperature Composites, Reno, Nevada, edited by F. Lemkey et al. (MRS, Pittsburgh, 1988); E. Drescher-Krasicka, J. A. Simmons, and H. N. Wadley, "Fast Leaky Modes on Cylindrical Metal-Ceramic Interfaces," QNDE 9A 173-181 (1989).